pc computer used under $500.00 for music only

And also keep in mind that it is quite possible to get a very capable brand new laptop for that kind of money. Check out BestBuy, NewEgg, TigerDirect for great deals on new equipment...

-RW-

Depending on the horsepower you need you can get a nice Atom based PC for less than $500. Zotac makes nice ones. Atom processors with hardware acceleration can easily handle 1080p movies let alone high res FLAC files. I personally use two of them for my audio though I will be making a CAPS in the near future for my main listening room where I want the best sound quality.

Mojo Audio modded Mac-Mini.
Thrilled with ours!!

The PC is easy with that budget. I got an Acer Aspire, put in an SSD 250gb drive and downgraded to windows 7. Final move was to buy Jriver. There went $500.

However, I spent almost as much on a DAC with USB input. Your system will only be as good as the signal coming out of the PC. If you have a desktop, you could install a good soundcard. However, I really don't think there is a soundcard I would buy over my Schiit Bifrost.

The other option is to get an SPIDF adaptor (Music Fidelity V Link) to convert USB to digital and then go into your digital input in your system (if you have one)

Asus EEE Box with the Atom processor. About the size of a router and no fan. Strip down the software to minimum and install Fidelizer.